This invention relates generally to golf clubs, in particular, to so-called metal wood-type golf clubs.
Golf clubs known as “woods” traditionally have a head made of a suitable wooden material such as maple or persimmon attached to one end of an elongated shaft. These traditional wood club heads are usually solid and are shaped with their weight properly distributed about their center of gravity to maximize performance. Golf club “wood” heads have also been formed of suitable metals such as stainless steel and titanium. Metal wood heads are usually hollow so as to minimize weight while leaving the maximum amount of material available for the structural components of the head. Various attempts have been made to distribute weight in metal wood heads with respect to their centers of gravity so that the performance is maximized. Such attempts have included placing different types and numbers of weight members at different locations on or inside the metal heads. Examples of such attempts are disclosed in prior U.S. Pat. No. 4,869,507 to Sahm; U.S. Pat. No. 5,058,895 to Igarashi; U.S. Pat. No. 5,141,230 to Antonious; U.S. Pat. No. 5,219,408 to Sun; and U.S. Pat. No. 5,851,160 to Rugge, et al.
The Sahm patent teaches that lowering the center of gravity of a club head would tend to add more loft to a golf shot. Igarashi teaches that perimeter weighting increases the moment of inertia of a wood type club about its center of gravity. The increased moment of inertia causes the club to resist twisting when a ball is not struck at the “sweet spot”, that is, the point on the club face at which a line normal to the face passes through the club head's center of gravity. Reducing the twisting causes the ball to travel with less loss of directional control. Antonious teaches a hollow metal wood club having an internal weighted mass integrally formed with the under side of the upper section of the club head shell that is combined with another mass placed directly behind or adjacent to the center of percussion of the ball striking face. Sun teaches threading a plurality of individual weights into the sole plate of the club head from outside. Rugge teaches use of a weight pad located within the cavity of the hollow metal head along the sole portion. The weight pad is positioned so that the center of gravity of the golf club head is located beneath the center of the impact face and closer to the heel portion than the toe portion. According to Rugge, by positioning the weight pad closer to the heel portion, the moment of inertia about the center of gravity of the golf club is increased while minimizing the increase in moment of inertia about the shaft axis. Among the disadvantages of the aforementioned prior art patents, however, is that weight pads that are integrally formed or attached inside the cavity of the golf club head such as disclosed in Antonious and Rugge cannot be adjusted once the club head is assembled. Conversely, externally attached inserts such as disclosed in Sun mar the appearance of the sole plate of the club and may come loose during use.